I'll add this to suggestions list, but it's more complicated than you think. How and whether you can center the menu depends on the rest of the page that is out of control of Easy Button & Menu Maker:- whether you use good, standards compliant code or quirks mode- whether you use css that can affect menu positioning- whether you've placed the menu inside an element that has sufficient width to center the menu

If everything in the page is done correctly however, the menu can be centered with basic CSS: